Field of the Invention
The invention relates to a method and an arrangement for controlling the power of a transmission amplifier, in particular of a transmission amplifier in a mobile radio terminal.
FIG. 3 shows an outline circuit diagram of a conventional arrangement for controlling the power of a transmission amplifier PA. The signals sig which are supplied to the transmission amplifier PA and are to be amplified are amplified on the basis of a control parameter reg, which is supplied to the transmission amplifier PA and represents a measure of the gain or the gain level/factor, and are supplied to a directional coupler RK. The directional coupler RK outputs a small portion of the power supplied from the transmission amplifier PA to the antenna ANT and supplies it to a radio frequency detector HFD, which converts this power into a DC voltage. This DC voltage value produced in this way is supplied as an actual valuexe2x80x94(act)xe2x80x94to a comparison device V, where it is compared with a nominal valuexe2x80x94(nom)xe2x80x94which is predetermined by a control device, such as a microcontroller in a mobile radio terminal. The comparison results in a control parameter reg being output, which sets the gain of the transmission amplifier PA such that the actual value corresponds to the nominal value nom. To this end, the gain factor is raised or lowered based on the difference between the nominal value and the actual value. The majority of the power is supplied from the directional coupler RK to the antenna ANT, from which this power is transmitted in the form of radio-frequency signals. Such conventional power control loops for a transmission amplifier operate well over a narrow predetermined power band.
However, in order to improve the spectrum utilization and to increase the operating time of the mobile radio appliance, modern mobile radio terminals can be operated at different transmission power levels. For example, depending on the power class of the mobile radio terminal, the transmission power of GSM (Global System for Mobile Communication) mobile radio terminals can be varied within a range of 20 and 30 dB. Furthermore, the transmission power of mobile radio terminals which operate using a time slot mode, such as GSM mobile radio terminals, must be controlled on the basis of a predetermined time slot structure. In this case, it is particularly important in order to produce a transmission pulse (burst) to set the transmission amplifier in accordance with a fixed predetermined nominal time/power curve (power ramping), which likewise necessitates a wide power dynamic range.
These two requirements for controlling the power of a transmission amplifier can no longer be satisfied reliably by conventional methods or arrangements. In particular, reliable power detection by means of an RF detector over a wide power band is scarcely feasible using simple means. This problem is further exacerbated when controlling the power of a multiband or multimode mobile radio terminal since, in this case, the number of transmission power levels is further increased, and different nominal time/power curves can be specified. Future CDMA mobile radio terminals will also require transmission power control over a very wide power band.
The invention is thus based on the object of specifying a method and arrangement for controlling the power of a transmission amplifier, which allow the power to be controlled in a simple manner and nevertheless reliably over a wide power band. According to the invention, a portion of the power emitted from a transmission amplifier is output by means of a coupling element, and for a desired transmission power level, which is less than a predetermined limit value, a further portion of the power is additionally output by means of a controlled switching device, and the output power is used for controlling the transmission amplifier.
The invention is accordingly based on the idea of outputting a relatively small portion of the power by means of a coupling element in a first case in which the desired transmission power is greater than a predetermined limit value, and of using this small portion to control the power of the transmission amplifier. In a second case, in which the desired transmission power is below a specific limit value, a relatively large portion of the power emitted from the transmission amplifier is additionally output via a switching device, and is used to control the power of the transmission amplifier.
This means that, in both cases, the absolute value of the output power is at least in a similar order of magnitude, and the components which are used for further processing the output power to form a control parameter for the transmission amplifier, in particular the radio-frequency detector, can thus be operated in a relatively narrow band, thus ensuring that the power can be controlled more reliably and with less complexity.